iCloud

Add or remove an SMS number

1. Go to your Apple ID account page and enter your Apple ID and password.
2. In the Security section, click Edit.
3. Click Add a Trusted Phone Number. 
4. To add a number, enter the phone number and verify it with a text. 
5. To remove a number, click  next to the phone number you want to remove. 

If you are locked out of your Apple ID account you can go to https://iforgot.apple.com

This will provide you with the recovery steps you put in place for this situation.

Here are some support articles that should help:

If you forgot your Apple ID password - Apple Support

If you forgot the answers to your Apple ID security questions - Apple Support

If your Apple ID has been locked or disabled – Apple Support